92 Sub Tail lights not working

The tail lights and license plate lights are not working but the rear turn signals, back-up and brake lights work fine. The front parking and headlights work fine. None of the fuses are blown and testing at the rear coupler, the yellow tail light wire that comes from the firewall has no power. My questions are: 1] could this be a relay 2] where is it located? 3] how do you tell if a relay is bad?

I have a '92 chevy Suburban 1500 and I pulled a trailer the other week, only to discover a couple weeks later I had this problem. I'm baffaled that all my lights including the front lights are fine, but only the two rear tail lights are out. Any thoughts would be appreciated.

You'd be surprised at the people who don't. There usually isn't a relay for the tail lights, just power and ground.

Do you have a multi-meter that can read 12 volts and resistance?

You need to check for 12 volts at a socket. If there is no 12v (and your post suggests there isn't), you have a blown fuse, or a broken wire. You checked the fuses, so it appears the wire may be damaged.

However, not sure which yellow connector your talking about. If it is a body connector, your on the right track. If it is the trailer connector, there usually are separate fuses for that connector.

So, if there happens to be 12v at the sockets, your ground is missing (broken wire/dirty connection). The ground wire should be black.

Thanks Ray, I'm sure you're right but changing the fuse and then the bulbs was the first thing I tried

The light green (I said yellow) wire that comes from a "block" (not sure what you call that) mounted on the firewall above the stearing column to the back bumper connector or splice before it splits off to the R/L lights and the license plate, is "dead". I'm thinking the bad connection or break must be buried in the dash somewhere and an <easy> fix would be to splice a connecting wire from the front parking lights which work fine, to the dead wire that runs to the back. Clearly, I'm not a mechanic, but a building contractor used to finding solutions that can resolve the problem and get the job done....

You'd be surprised at the people who don't. There usually isn't a relay for the tail lights, just power and ground.

Do you have a multi-meter that can read 12 volts and resistance?

You need to check for 12 volts at a socket. If there is no 12v (and your post suggests there isn't), you have a blown fuse, or a broken wire. You checked the fuses, so it appears the wire may be damaged.

However, not sure which yellow connector your talking about. If it is a body connector, your on the right track. If it is the trailer connector, there usually are separate fuses for that connector.

So, if there happens to be 12v at the sockets, your ground is missing (broken wire/dirty connection). The ground wire should be black.

Your issue most likely isn't fuse-related because the front running lights work. I'm also inclined to say you don't have an issue under the dash because the front running lights work. I'm not sure where the junction block is that would send the lights to the front and the back, but it's most likely on the drivers side of the truck. If you have a Haynes or Chilton manual, the wiring diagrams should be in the back complete with color codes for the wires. I'd work my way from the back of the truck forward looking for power at each junction the running light wire comes to.

I know on my 91 Suburban (which is based off the 80s bodystyle and not yours) there is a multi-pin connector directly below the rear cargo doors just behind the trailer hitch. I don't think that changed drastically from my truck. At this junction is where the trailer lights are picked up. I'd check there and if possible, pull the T-tap for the trailer lights out of the mix just to make sure it isn't that.

Actually, on some trucks, there would be 3 fuses (more if you include the wiring for the trailer connector), there will be a fuse for the front running lights, one for the left rear (which includes the plate lights) and a fuse for the right rear running light. pk 's truck appears to have one lead going from the dash to the rear and then spliting into the left and right sides; therefore, probably one rear circuit.
The reason the front and rear are separate, is due to the danger of damage to the rear wires from normal truck use.

pk, does your truck have 2 fuse panels? My truck has one under the hood and one at the end of the dash, my old truck had one under the hood and one under the middle row seats.

Actually, on some trucks, there would be 3 fuses (more if you include the wiring for the trailer connector), there will be a fuse for the front running lights, one for the left rear (which includes the plate lights) and a fuse for the right rear running light. pk 's truck appears to have one lead going from the dash to the rear and then spliting into the left and right sides; therefore, probably one rear circuit.
The reason the front and rear are separate, is due to the danger of damage to the rear wires from normal truck use.

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You are absolutely correct on your assertion; however, you have the wrong bodystyle/generation. As far as I know, GM did not start doing separate fusing per side and separate fuses for the trailer lighting until 1998.5/1999. Before that, all the running lights and turn signals were on one fuse.